Amoebic dysentery is a type of diarrheal disease that affects millionsaround the globe annually. Passed around by contaminated water,amoebas get into people's intestines, causing bloody diarrhea. If leftuntreated, these single-cell organisms can eventually perforate theintestines, spread throughout the body and kill the host. As Rose Hobanreports, researchers are learning more about the amoeba's ability tooutwit the body's immune system.  

When a foreign material, likean amoeba, enters the body, immune cells don't recognize the proteinson the surface of the cell... that's because they're foreign. So immuneantibodies attack these foreign proteins, and are able to neutralizethe invading cell. But amoebas can evade the human immune system.

JohnsHopkins biochemist Sin Urban says these simple organisms have evolved asophisticated method to escape this immune attack. "What the amoebadoes, [is] it takes all these proteins once they become attacked byantibodies, and it shuttles all of them to the back of the cell andjettisons them in a little ball," Urban explains. "So essentially, it'staking all of the things that our immune system is attacking, andjettisons it, and essentially gets away scot free." The antibodiescontinue to attack the protein, while leaving the amoeba alone.

Thekey to creating this immune decoy is the rhomboid enzymes produced bythe amoeba. Enzymes are present in almost every living thing. Urbanexplains that they facilitate chemical reactions in - and on - cells."We found out that the rhomboid enzyme is usually on the surface, butduring this jettisoning process, it actually forms a tight seal aroundthe base of this little ball that's being released. Being an enzyme,and being in that part of the cell during this release process, wethink it might actually be involved in release of this little ball ofsurface proteins."

Urban is trying to learn more about therole of rhomboid enzymes in this decoy process. He says in the future,rhomboids could end up being a good target for new medications to treatamoebic dysentery.

Urban's research is in a recent issue of Genes and Development.